GELLERMAN: If you’re going to live in Norway you have to be a hardy creature, capable of enduring long, dark winters. But adaptation to the cold climate can sometimes be deadly if things warm up. Reporter Ari Daniel Shapiro has our story.

BRETTEN: Looking for something that’s dark, brown and hairy.

SHAPIRO: That’s Tord Bretten, a park ranger in Dovrefjell, a mountain range in south central Norway. And he’s looking for muskoxen, or ovibos moschatus. He walks across spongy lichens until finally he stops, and scans the landscape.

SHAPIRO: Did you spot one, Tord?

BRETTEN: Yes, we have one male between the small stream and the biggest snow patch. That black spot.

SHAPIRO: Oh, that black spot. Can I look through your binoculars?

BRETTEN: Yes.

SHAPIRO: This male weighs close to half a ton. Two horns curl out of his shaggy head. He’s healthy and robust, like the other 300 or so animals in the herd. But back in 2006, Bretten had a mystery on his hands. Dead muskoxen were turning up everywhere.

BRETTEN: I was out everyday and we found muskoxes all the time.

SHAPIRO: Dead.

BRETTEN: Yes, and some of them we saw – we had a small herd of five here, I saw everyday for three days. And the third day, there were just four. One of them had died, and she was, I saw her, it was a fully-grown cow. I saw her the day before, and she didn’t look ill at all. Next day she was just dead.

SHAPIRO: Twenty-five dead animals were found that season. Another 60 went missing from the herd, and they were presumed dead.

BRETTEN: Oh, I was a bit worried that the population could get extinguished. I grew up down here and I’m used to them, I like them. I’ve seen them almost all my life. It would be a pity if they disappear.

SHAPIRO: There was no obvious cause of death. So Bretten invited Bjørnar Ytrehus to come visit. He’s a vet with the Norwegian Veterinary Institute, and he was just as puzzled. The animals had plenty of fat reserves. Their bellies were full of food. It looked like they’d just dropped in place. But then he looked at their lungs.

YTREHUS: The lower part of the lungs was dark, firm and with a lot of liquid inside, a bloody, watery, cut surface. These were signs of pneumonia.

SHAPIRO: A pneumonia caused by Pasteurella bacteria. Ytrehus had seen this kind of thing in sheep and reindeer before, and he knew that it’s usually related to some kind of stress. As for what had stressed the muskoxen:

YTREHUS: The temperature in this period had reached an all-time high.

SHAPIRO: It was the fall, and so the muskoxen had already grown in their warm winter wool. They were overheating.

YTREHUS: When they experience heat, they have to pant to get rid of the heat. (Demonstrates musk ox panting). And this will accumulate bacteria that normally are found in the throat into the lungs.

SHAPIRO: Which is what led to the pneumonia. Usually, the cooler, drier mountains of Dovrefjell are an ideal place for the musk oxen. In fact, since the 2006 die-off when a third of the animals were lost, the temperatures have cooled and the herd’s recovered. But Ytrehus worries that it could happen again.

YTREHUS: As the climate changes, the climate on the mountain will also change in a warmer and wetter direction.

SHAPIRO: It’s worth pointing out that muskoxen disappeared from Norway after the last ice age once it got too warm here. So the muskoxen in Dovrefjell today were not originally from Norway. They were brought over from Greenland back in the 40s. And they were deposited in Dovrefjell – one of the few places in Norway today where the climate’s right for them. Bjørnar Ytrehus’ great-uncle was partly responsible for the transport of these animals. He was working in Greenland in the 40s and 50s.

YTREHUS: He was lending his sled dogs to the people who wanted to catch calves. He regarded that as one of the worst things he had done in his life.

SHAPIRO: Why?

YTREHUS: Oh, because they killed the adult muskoxen to capture the calves. And the calves were crying for their mothers. And they brought the calves onboard the ship and took it back to Norway. I think he regard that as a terrible thing to do now that he’s an old man, but I’m sort of comforting him in that it is great that we have muskoxen on Dovre. And that they may have some use for us now.

SHAPIRO: Ytrehus sees these musk oxen as environmental sentinels, warning us about what could happen to animals in a world that’s getting warmer and wetter. The muskoxen were transplanted here to recall Norway’s past. But they may have more to say about the future. For Living on Earth, I’m Ari Daniel Shapiro.

GELLERMAN: Our muskoxen story comes to us from the series One Species at a Time.
It's produced by Atlantic Public Media with support from the Encyclopedia of Life. For more, follow the herd to our website LOE dot org.